Paper/Spigot-Server-Patches/0211-Properly-handle-async-calls-to-restart-the-server.patch

From 8a440893d6d24e50beb7b2af0e00f2563142893a Mon Sep 17 00:00:00 2001
From: Zach Brown <zach.brown@destroystokyo.com>
Date: Fri, 12 May 2017 23:34:11 -0500
Subject: [PATCH] Properly handle async calls to restart the server

The watchdog thread calls the server restart function asynchronously. Prior to
this change, it attempted to do several non-safe operations from the watchdog
thread, rather than the main. Specifically, because of a separate upstream change,
it causes player entities to be ticked asynchronously, among other things.

This is dangerous.

This patch moves the old handling into a synchronous variant, for calls from the
restart command, and adds separate handling for async calls, such as those from
the watchdog thread.

When calling from the watchdog thread, we cannot assume the main thread is in a
tickable state; it may be completely deadlocked. In order to handle this, we mark
the server as stopping, in order to account for situations where the server should
complete a tick reasonbly soon, i.e. 99% of cases.

Should the server not enter a state where it is stopping within 10 seconds, We
will assume that the server has in fact deadlocked and will proceed to force
kill the server.

This modification does not force restart the server should we actually enter a
deadlocked state where the server is stopping, whereas this will in most cases
exit within a reasonable amount of time, to put a fixed limit on a process that
will have plugins and worlds saving to the disk has a high potential to result
in corruption/dataloss.

diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
index 40514d042..f0743e6cc 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -70,6 +70,7 @@ public abstract class MinecraftServer implements ICommandListener, Runnable, IAs
     public WorldServer[] worldServer;
     private PlayerList v;
     private boolean isRunning = true;
+    private boolean isRestarting = false; // Paper - flag to signify we're attempting to restart
     private boolean isStopped;
     private int ticks;
     protected final Proxy e;
@@ -488,7 +489,7 @@ public abstract class MinecraftServer implements ICommandListener, Runnable, IAs
         if (this.v != null) {
             MinecraftServer.LOGGER.info("Saving players");
             this.v.savePlayers();
-            this.v.u();
+            this.v.u(isRestarting);
             try { Thread.sleep(100); } catch (InterruptedException ex) {} // CraftBukkit - SPIGOT-625 - give server at least a chance to send packets
         }
 
@@ -545,10 +546,18 @@ public abstract class MinecraftServer implements ICommandListener, Runnable, IAs
         return this.isRunning;
     }
 
+    // Paper start - allow passing of the intent to restart
     public void safeShutdown() {
+        safeShutdown(false);
+    }
+
+    public void safeShutdown(boolean isRestarting) {
         this.isRunning = false;
+        this.isRestarting = isRestarting;
     }
 
+    // Paper end
+
     // Paper start - Further improve server tick loop
     private static final int TPS = 20;
     private static final long SEC_IN_NANO = 1000000000;
@@ -1612,6 +1621,7 @@ public abstract class MinecraftServer implements ICommandListener, Runnable, IAs
         return this.ab;
     }
 
+    public final Thread getServerThread() { return this.aI(); } // Paper - OBFHELPER
     public Thread aI() {
         return this.serverThread;
     }
diff --git a/src/main/java/net/minecraft/server/PlayerList.java b/src/main/java/net/minecraft/server/PlayerList.java
index bc2322e62..a43588598 100644
--- a/src/main/java/net/minecraft/server/PlayerList.java
+++ b/src/main/java/net/minecraft/server/PlayerList.java
@@ -1361,10 +1361,15 @@ public abstract class PlayerList {
         entityplayer.playerInteractManager.b(world.getWorldData().getGameType());
     }
 
+    // Paper start - Extract method to allow for restarting flag
     public void u() {
+        u(false);
+    }
+
+    public void u(boolean isRestarting) {
         // CraftBukkit start - disconnect safely
         for (EntityPlayer player : this.players) {
-            player.playerConnection.disconnect(this.server.server.getShutdownMessage()); // CraftBukkit - add custom shutdown message
+            player.playerConnection.disconnect(!isRestarting ? this.server.server.getShutdownMessage() : org.spigotmc.SpigotConfig.restartMessage); // CraftBukkit - add custom shutdown message // Paper - add isRestarting flag
         }
         // CraftBukkit end
         // Paper start - Remove collideRule team if it exists
@@ -1375,6 +1380,7 @@ public abstract class PlayerList {
         }
         // Paper end
     }
+    // Paper end
 
     // CraftBukkit start
     public void sendMessage(IChatBaseComponent[] iChatBaseComponents) {
diff --git a/src/main/java/org/spigotmc/RestartCommand.java b/src/main/java/org/spigotmc/RestartCommand.java
index 49768734d..e1bc3e64e 100644
--- a/src/main/java/org/spigotmc/RestartCommand.java
+++ b/src/main/java/org/spigotmc/RestartCommand.java
@@ -45,88 +45,119 @@ public class RestartCommand extends Command
         AsyncCatcher.enabled = false; // Disable async catcher incase it interferes with us
         try
         {
-            if ( script.isFile() )
-            {
-                System.out.println( "Attempting to restart with " + SpigotConfig.restartScript );
+            // Paper - extract method and cleanup
+            boolean isRestarting = addShutdownHook(script);
+            if (isRestarting) {
+                System.out.println("Attempting to restart with " + SpigotConfig.restartScript);
+            } else {
+                System.out.println( "Startup script '" + SpigotConfig.restartScript + "' does not exist! Stopping server." );
+            }
 
-                // Disable Watchdog
-                WatchdogThread.doStop();
+            // Stop the watchdog
+            WatchdogThread.doStop();
 
-                // Kick all players
-                for ( EntityPlayer p : (List< EntityPlayer>) MinecraftServer.getServer().getPlayerList().players )
-                {
-                    p.playerConnection.disconnect(SpigotConfig.restartMessage);
-                }
-                // Give the socket a chance to send the packets
-                try
-                {
-                    Thread.sleep( 100 );
-                } catch ( InterruptedException ex )
-                {
-                }
-                // Close the socket so we can rebind with the new process
-                MinecraftServer.getServer().getServerConnection().b();
-
-                // Give time for it to kick in
-                try
-                {
-                    Thread.sleep( 100 );
-                } catch ( InterruptedException ex )
-                {
-                }
+            shutdownServer(isRestarting);
+        } catch ( Exception ex )
+        {
+            ex.printStackTrace();
+        }
+    }
 
-                // Actually shutdown
-                try
-                {
-                    MinecraftServer.getServer().stop();
-                } catch ( Throwable t )
-                {
-                }
+    // Paper start - sync copied from above with minor changes, async added
+    private static void shutdownServer(boolean isRestarting)
+    {
+        if (MinecraftServer.getServer().isMainThread())
+        {
+            // Kick all players
+            for ( EntityPlayer p : com.google.common.collect.ImmutableList.copyOf( MinecraftServer.getServer().getPlayerList().players ) )
+            {
+                p.playerConnection.disconnect(SpigotConfig.restartMessage);
+            }
+            // Give the socket a chance to send the packets
+            try
+            {
+                Thread.sleep( 100 );
+            } catch ( InterruptedException ex )
+            {
+            }
 
-                // This will be done AFTER the server has completely halted
-                Thread shutdownHook = new Thread()
-                {
-                    @Override
-                    public void run()
-                    {
-                        try
-                        {
-                            String os = System.getProperty( "os.name" ).toLowerCase(java.util.Locale.ENGLISH);
-                            if ( os.contains( "win" ) )
-                            {
-                                Runtime.getRuntime().exec( "cmd /c start " + script.getPath() );
-                            } else
-                            {
-                                Runtime.getRuntime().exec( new String[]
-                                {
-                                    "sh", script.getPath()
-                                } );
-                            }
-                        } catch ( Exception e )
-                        {
-                            e.printStackTrace();
-                        }
-                    }
-                };
+            closeSocket();
 
-                shutdownHook.setDaemon( true );
-                Runtime.getRuntime().addShutdownHook( shutdownHook );
-            } else
+            // Actually shutdown
+            try
             {
-                System.out.println( "Startup script '" + SpigotConfig.restartScript + "' does not exist! Stopping server." );
+                MinecraftServer.getServer().stop();
+            } catch ( Throwable t )
+            {
+            }
+        } else
+        {
+            // Mark the server to shutdown at the end of the tick
+            MinecraftServer.getServer().safeShutdown(isRestarting);
 
-                // Actually shutdown
-                try
-                {
-                    MinecraftServer.getServer().stop();
-                } catch ( Throwable t )
-                {
-                }
+
+            // wait 10 seconds to see if we're actually going to try shutdown
+            try
+            {
+                Thread.sleep(10000);
+            }
+            catch (InterruptedException ignored)
+            {
             }
+
+            // Check if we've actually hit a state where the server is going to safely shutdown
+            // if we have, let the server stop as usual
+            if (MinecraftServer.getServer().isStopped()) return;
+
+            // If the server hasn't stopped by now, assume worse case and kill
+            closeSocket();
             System.exit( 0 );
-        } catch ( Exception ex )
+        }
+    }
+
+    // Paper - Split from moved code
+    private static void closeSocket() {
+        // Close the socket so we can rebind with the new process
+        MinecraftServer.getServer().getServerConnection().b();
+
+        // Give time for it to kick in
+        try
         {
-            ex.printStackTrace();
+            Thread.sleep( 100 );
+        } catch ( InterruptedException ex )
+        {
+        }
+    }
+    // Paper end
+
+    // Paper - copied from above and modified to return if the hook registered
+    private static boolean addShutdownHook(final File script) {
+
+        if (script.isFile()) {
+            Thread shutdownHook = new Thread() {
+                @Override
+                public void run() {
+                    try {
+                        String os = System.getProperty("os.name").toLowerCase(java.util.Locale.ENGLISH);
+                        if (os.contains("win")) {
+                            Runtime.getRuntime().exec("cmd /c start " + script.getPath());
+                        } else {
+                            Runtime.getRuntime().exec(new String[]
+                                    {
+                                            "sh", script.getPath()
+                                    });
+                        }
+                    } catch (Exception e) {
+                        e.printStackTrace();
+                    }
+                }
+            };
+
+            shutdownHook.setDaemon(true);
+            Runtime.getRuntime().addShutdownHook(shutdownHook);
+            return true;
+        } else {
+            return false;
         }
     }
 }
-- 
2.13.0